text:
For a private GA pilot, when is an endorsement needed for a particular type of aircraft?
If I've done my training say 85% in a C152 and 15% in a C172, then upon my earning my PPL, what am I allowed to fly legally?  I assume the 152, but not sure about the 172. Is this indicated somehow in my logbook? When is a separate check out required for a new airplane and assuming the same type (i.e., SEL, fixed gear, fixed pitch prop, non pressurized, etc.), what would this typically entail?  Is this an FAA requirement or a liability requirement for clubs, etc.?

There are two aspects here, one what is required legally and then what may be required locally.
From a legal standpoint (in your case) the basic PPL will allow you to fly single engine, fixed pitch prop, under 200HP, fixed gear aircraft. If you want to go over 200 HP you will need a High Performance check out and log book endorsement. For a constant speed prop/folding gear/movable flap (all 3 are required to require this endorsement) plane you will need a complex endorsement in your log book. You may want to fly something like a Piper Cub which will require a tail wheel endorsement. If you are lucky enough (and have the funding to do so) you may find your self in a small pressurized single (or twin) like the Piper Meridian or TBM 900 these planes will require a high altitude checkout as well. AOPA has a nice summary of the endorsements here. If you want the full FAA FAR regs you can find them here.
Now as for a club or school that depends on a variety of factors including their insurance and their personal limits. I'll offer some personal experience which seems to be pretty par for the course. The flight school I fly from requires a checkout in type from every new renter before you can fly it even if you have a PPL and the proper endorsements. They don't have an official amount of time but it usually takes about an hour with an instructor. The former flight school I was at had the same deal with the exception of their Saratoga which they also required an instrument rating (along with their checkout).
My buddy's flight club is somewhat similar. They require a check out in their Archer and Dakota to fly solo. They also have a Lance which they require 25 hours time in type and a 5 hour check out in the plane.
As for your log book you should be logging the full type of aircraft for every flight. For example when I fly the Warrior I make sure to note PA-28-161 and the Archer I fly is noted as PA-28-181 when I record hours this way I can note time in type at a detailed level.
For what its worth with the PA-28 airframe it seems that some places to allow you to fly the lower rated planes if you are checked out in the higher power ones. The same basic frame was built in a 140, 160, 180 and 235HP variant over the years and has little differences aside from useful load and V speeds. For example at the place I go if you are checked out in the Archer first you are allowed to fly the Warrior with out a checkout.
This will also extend to ownership should that be the path you go down. In that case you insurance company may require a certain amount of hours of time in type before you are allowed to solo your plane. Keeping that in mind you are not actually prevented from buying the plane and will be insured under the stipulation that the first hours in the plane are with an instructor. When a buddy of mine (instrument rated and close to 600 hours at the time) upgraded from his 72 Archer to a 95 Saratoga HP his insurance company mandated he do 25 hours in type with an instructor before taking the plane solo. The first 25 hours he flew his plane were with an instructor (this included transporting the plane from the factory in Vero Beach to his home field).
You can legally fly both planes once you have your PPL. What someone will let you fly should be pretty well addressed above. Neither the 172 or 152 requires a specific type rating like larger planes do.

Good answer. Note that no special endorsement is needed for a non-complex aircraft that has either a constant speed prop, flaps, or retractable gear or any two of the same. The definition of complex is the combination of all three.

Answer has been updated to reflect

Just curious - you mention the requirement for 10 hours in type for the Lance and 25 with a club CFI. What if you already have 25+ hours solo time in type - would they accept your logged time, or would they still require time with their CFI? I realize that this is very club specific, so probably wouldn't rate a question of its own. I suppose at a general level, it could be a stand-alone question.

Thanks for the answer.  Just to confirm, in the eyes of the FAA, I'm legal to fly any SEL, fixed pitch, under 200 hp, no gear etc., with a PPL, regardless of the make, high wing, low wing, etc.  Practically speaking, however, any rental or club situation would likely be more restrictive and require a check out, probably for any aircraft they own.  Is that correct?

@FreeMan i was mistaken (and have updated my answer) according to their site they require 25 hours time in type and a 5 hour checkout in their lance, but this is specific to them.

@PJNoes yes you are legal to fly regardless of make make high/low wing etc. Except tail draggers and sea planes, they require ratings.


text:
What is significant about the number 8069 ft?
On a sectional chart legend, the airport icon with a solid magenta or blue disk is labeled as "Hard surfaced runways 1500 ft to 8069 ft in length".  This seems like an extraordinarily arbitrary number to use as the upper limit before a different symbol is used.  When I convert this to meters, or yards, or furlongs, or any other common unit, it doesn't correspond to any even number so it doesn't seem like a conversion from another system of units.  What is the reason for this unusual dimension for a runway length?

Apparently you aren't the only person who wondered this; the FAA actually has it in an FAQ:

What is the significance of a runway 8069 feet in length and why are two different aerodrome symbols used to depict hard surface runways on
  Sectional charts?
For purposes of airport depiction, specialists
  represent a runway between 7970 and 8069 feet in length as 8000 feet,
  which equates to a line 0.192 inches in length on the Sectional chart
  scale. In this case, a circular aerodrome symbol is used.
If a runway
  is between 8070 and 8169 feet in length, specialists round to 8100
  feet, which equates to a line 0.1944 inches in length on the sectional
  chart scale. This line is too long to fit into the largest circular
  aerodrome symbol FAA has available. Therefore, specialists place a
  line-work around the runway pattern forming a polygon (enclosed shape)
  for anything over 8069 feet in length.
Specialists also place these
  polygons around the runway pattern of aerodromes with multiple runways
  that are less than 8069 feet, in cases where the multiple runway
  pattern does not fit into the largest, circular aerodrome symbol.

I think that's only a partial explanation.  It gives the impression that it's simply something to do with how rounding is applied and the practicalities of drawing charts at a particular scale.  And that rounding is biased so that rounding downwards is more likely than rounding upwards.  But doesn't actually explain why the rounding works that way to begin with.  I imagine that if they used a more traditional rounding approach (8050-8149 -> 8100) then 8049 would be the "magic" number.  Why did they decide to round from 8069 instead?

Apparently, when performing some calculations for recommended runway length for a given configuration, "lengths of 30 feet and over are rounded to the next 100-foot interval."... and given the importance of not running out of runway, that does seem to make more sense than rounding +/-50.

Aeronautical Chart User's Guide: "Runway length is shown to the nearest
100’, using 70 as the rounding point;
a runway 8070’ in length is charted as 81, while a runway 8069’
in length is charted as 80."

@RyanMortensen Is this different from just subtracting 20 feet before rounding to the nearest 100?

@Random832 - Nope.

Wow, so it really is arbitrary.

It's arbitrary, but it errs on the side of caution. If the runway is slippery and you're on the heavier (but legal) side, and you know you need 8000' to land, I'd rather know that I might have as much as 8069' instead of only 8050'. Those 19' feet could make a huge difference in injury, damage & paperwork.

@FreeMan But you could also end up with only 7070 feet

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
Why do extra flight crew members sit in the cockpit during takeoff/landing?
I have observed this many times for long haul flights where they have extra cockpit crew: during takeoff they all gather in the cockpit and then disperse to their rest areas. They meet again somewhere halfway to hand off flying responsibilities and then gather again before landing. Usually approximately half an hour after/before takeoff/landing.
One way of thinking is, if you are going to rest, rest from the beginning. Just take over your duties when your turn comes up. Why even bother visiting cockpit if you are going to be there only for first 30 minutes or so of the flight.
I understand takeoff/landing are most critical phases of the flight where things can go wrong. But then airline have deemed that whoever is flying the plane at that point is fully capable of flying or in other words fully accredited crew is managing the flight.
Is there any other reason why all the crew has to meet in the cockpit during these phases?

There'a a few reasons for this:
Safety:
During takeoff and landing, everyone should be buckled into a secure seat. They have these seats in the cockpit, and in large aircraft, they're actually very comfortable. Laying down in a crew bed would not be allowed during takeoff or landing (though it happens, off the record). Do note that these beds do indeed have belts that are similar to those on rolling hospital beds, but it's not intended that these be used during takeoff or landing. It would be very difficult to escape the small confined space of the crew bunks during an emergency. Though some crew areas have seats, these are typically not "safe" seats, and they are only meant for resting on while in level flight.
Redundancy:
If something goes wrong with one, or both, of the pilots flying, you would really regret letting the other two qualified pilots go lay down in the back of the plane. Safety comes first in aviation, and the pilots are there to support each other.
Extra Help:
Extra crew sometimes helps the flying crew, whether that be by looking up information, radio frequencies, airport identifiers, and so forth.
Socializing:
Pilots are (usually) pretty friendly to each other. They all share a common interest, and while some of the older pilots may be a bit grizzled, they all got into aviation for their love of aircraft. There's typically some pretty lively conversations in the cockpit. As noted in the comments, this is while on the ground, pre/post taxi. Even during flight operations, additional pilots may be in the cockpit assisting with spotting traffic, birds, and so forth. Conversation is limited somewhat during taxi, takeoff, landing, and all other flying activity below 10,000ft (or until at cruising altitude, if cruising altitude is <10,000ft),

Do you have any citations for this? There is no socializing below 10,000ft in accordance with the sterile cockpit rule and some (maybe all) crew bunks do have belts or restraints your other two points are logical although the copilot is generally considered the redundancy

@Dave Regarding socializing, that is on the ground (pre/post taxi). Regarding the bed belts, those are for keeping you in the bed during turbulent flight, and being knocked around while sleeping. It's not meant for restraining you during landing and takeoff. Beyond that, in the event of an emergency, evacuating a bunk (that takes a good bit of contortion to get into in many aircraft) is not very easy. There is similar reasoning to why you typically would stay above-deck rather than below-deck on a smaller boat during rough seas.

(And for citations, personal experience. I'm not a commercial pilot, but many of my family are, and I was able to sit and observe in the cockpit during many flights when I was a child, pre-9/11 of course.)

For those of us who like flying, it's the take-off and landing that are fun.  Also, it's good to have more sets of eyes looking for traffic especially close to the airport where it's likely to be busier.  And somebody keeping an eye on where you are on the glideslope/MDA/etc is handy: if the guy in the seat behind you seat yells, "Watch your altitude!" you will certainly check it! Also, if anything goes wrong, it's more dangerous closer to the ground, so that's a good time to have help.

@Dave Crew rest areas are not certified for occupancy during takeoff and landing.  Any seat used during takeoff and landing (Part 25.785(b)) must meet 16g crashworthiness requirements (25.562) and there's no way you can meet that lying down in a bed.

@user71659 that I understand, however a lot of crew rest areas (contrary to my previous link) also have seats

There's more to socializing than idle chit chat: the sterile cockpit rule doesn't prevent socializing. Indeed, working together is one of the best ways to socialize.

@Matt In particular, a belt on a bed will stop you lifting off the bed and hitting the ceiling; it won't do a lot to stop you sliding backwards and forwards and hitting the wall.

@Dave The picture in your link is an A380 flight crew rest compartment. The seat is 90 degrees to the direction of travel, so I highly doubt that it will meet 16g, as the lower half your torso will be slammed into the bed. Besides, you can't tell how the seat is supported to the structure. I think there's also an issue with having two escape paths that the flight crew areas may not meet (the cabin crew areas often do have two).

Thanks for all the comments! I updated the answer to include some of the great points you guys made.

Most B777 aircraft have two forward facing seats in the pilot crew rest area that are certified for occupancy during takeoff and landing.

Replacement crew attend the initial briefing to ensure that they have all required information for their leg of the flight.
Additional crew on the flight deck can provide additional assistance as shown when reviewing the response to the uncontained engine failure of Quantas QF-32 out of Singapore. Coincidentally, two qualified pilots were present in the flight deck and materially assisted with closing out alarms, evaluating the impact of the damage and reducing the time taken to only two hours before preparing for landing.
The ATSB final report, on page 38 makes the observation "supporting flight crew provided valuable input and assistance to the primary flight crew". While they acknowledge the primary crew would likely have responded similarly without their presence, it could have resulted in additional delay before landing.
It is trite that the crew on an aircraft is as small as the manufacturers and airlines can make them at acceptable risk. Any additional help is to the benefit of the primary crew discharging their responsibilities, and the additional crew as being committed to the same outcome as all other passengers.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can you be a monocular airline pilot in Europe?
I know this question has been asked before but it was for the US and I would like to know about Europe.
I was born with no vision in my left eye, and I have always wanted to become a commercial airline pilot, I have very good vision in my right eye. I just want to know if I could do it in Europe and if I would have any restrictions on my medical like not being able to fly internationally or fly big planes like the a380, and if it’s possible to become a captain. Or if it’s possible to get it without a soda, and would there be any differences. Or can you get a soda in Europe like the us.

Welcome to aviation.SE! As you said, this question has been asked and answered before, so can you clarify why you're still confused and what extra information you need? I don't think we can provide a compete list of every country that allows it, but are you interested in a specific country?

It’s more like if you could do it in Europe, and if there would be restrictions on where I could fly. Because it would be annoying if I only could fly in one country in Europe, and if I couldn’t fly big planes like the a380

I'm not sure that this is specific enough and fleshed-out enough to be an answer, but: IATA does publish a PDF of medical guidelines concerning flight crew, among others. Section 3.1.2 mentions inimal requirements to the necessary functions such as vision and hearing. I'm not a pilot myself, so I'm not sure how open this is to interpretation.

I think that’s only about the flight attendants, it was more like if I could become a commercial airline pilot

I appreciate this is your dream but you may have to accept that being a commercial pilot is just not for you. It's not necessarily a case of "the more you want it the more it will happen" it's simply down to safety. The use of both eyes is particularly important for depth perception & peripheral vision - two very important things in aviation. With that said there are a number of flying schools catering for disabled pilots so it may be worth getting in touch with them to see if it's possible to get a private licence.

But I think that you can get a soda for monocular pilots in the us. Maybe I could move to Europe with a faa medical class 1 with a soda, and then fly in European airspace.

I would be extremely surprised if you were allowed to have a medical without depth perception. IMO that is crucial to being safe in the sky and operating an aircraft.

UK CAA says

EASA MED.B.070 (e) states that “Applicants for a Class 1 medical certificate shall be required to have normal fields of vision and normal binocular function”.

Therefore, you will unfortunately have to move out of the EU to become an airline pilot.

What if I Then get a faa class 1 and then move back to Europe. Would I so be able to fly in European airspace for a European airline. Or can’t I get a soda in Europe

The person that speaks about two eyes being important for 'depth perception & peripheral vision' is talking rubbish. My ophthalmologist who teaches at Moorfields says one eye compensates for the lack of the second eye. CAA have understood this and wanted to change the rules but EASA stopped them. In Australia - hardly a country with a poor safety record - monocular commercial pilots are allowed to fly and have been for years. They have been sensible and understood this for years. I think in the US (but am not certain), it may be allowed too. But in Europe we are in the stone age, sadly because of nonsense like this based on pseudo science.

Welcome to the site! This does not really answer the question. Please take our tour (https://aviation.stackexchange.com/tour) to familiarize yourself with our guidelines.

Welcome to Aviation SE. While I agree with you I sad to tell this is not an answer by this Q&A site. Please read the help sections.

It actually DOES answer the stated question. Yes, it does so in the middle of a rant about why the European standard is a foolish one, but that's in the realm of up/downvotes, rather than closing as NAA. AKAICT.

Hello @Forest, welcome to aviation.stackexchange. In this community we value it when people disagree with a given answer and take the time to write a better answer; which may include explaining what is wrong in the other answer. But it's considered bad form and disrespectful to say other people are "talking rubbish". Be nice to other users that spend their valuable time in making this a better site, even if you disagree with them. You can use the edit function to rephrase your answer, and I encourage you to do so. For now I will vote your answer down.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can you become a commercial airline pilot in Europe while being monocular
I’m not sure if I could get a EASA medical class 1 while being monocular. But I think that you can get a soda in the us and I want to know, if I could take a FAA medical class 1 and then fly in Europe with a FAA. Or even better if I could get a soda in Europe and get a EASA medical class 1, and become a commercial airline pilot in Europe while being monocular.
I know this has been asked before but that only covers about getting the license, and I want to know if I could get a soda.

Pilot certificates don't give you permission to fly in a location, they give you permission to fly an airplane registered by that authority anywhere in the world. In other words, if you have an FAA pilot certificate you can fly a US registered airplane no matter where it is. If you have an FAA ATPL and appropriate class of medical you can work for any airline that flies US registered airplanes. The same is true for any licensing authority.
The reverse is not true, you could not get a FAA certificate and fly a UK registered airplane, for example, even if it was in the US. There are some cases where you can get a local certificate on the basis of another equivalent certificate, but I believe you always need to be able to pass the local medical.

There some who says that I could fly in Europe and I’m not sure if I would be able to fly a European registered airplane. Does anyone know if I could get a soda in Europe.

There's no such thing as a european registered airplane, every country has its own aviation authority that registers airplanes and issues licences/certificates, including medical certificates. Many countries are part of EASA, however you have to look at it in a country by country basis.

But can I get a soda in Europe and if not could I then take a FAA with a soda and fly in European airspace.

If you can get a licensing authority to issue you with a medical certificate and you get a pilots license from that authority then you can fly an airplane registered with that authority, it doesn't matter where it is.

Can you get a soda in Europe like the us

It depends on the authority, and the class you are going for. I don't know, honestly.

GdD, I think you're close to right about not being able to fly a UK registered airplane with an FAA pilot certificate. But, there is an exception: you can fly it in the U.S. An FAA pilot certificate allows you to fly any airplane in the U.S. (as long as it's legal to fly it in the U.S. at all), regardless of its country of registration.


text:
Is the physical MAX8 design bad because software is required for the aircraft to stay airborne?
I'm not an aviator by any means, but one thing that has come up in recent conversations with friends is that the MAX8 is inherently unsafe because alone, unpowered, the craft is not 'aerodynamically stable'.
As we understand it, the new engine configuration means that the plane has a tendency to point upwards, requiring software to constantly point the nose down (which also seems kinda sketchy, cuz.. software). I imagine that if there was nothing to run the software, the nose would raise higher and higher until the whole thing was trying to backflip. I understand it wouldn't go totally vertical, but I guess maybe enough to stall or something else just as bad.
Is this true and is this the only aircraft with this kind of 'software or bust' design?
Edit:
My apologies, this question is probably pretty terrible for the majority of the people on this particular stack, but the thought has come up and been validated enough in conversations that I thought to ask folks here to get a better idea and/or be proven wrong (as has happened). I had no idea about phugoid or any of that kind of thing. I only really have "heavier engines cause the craft to pitch upward requiring software to point downward" and "software requires power to run" to base any kind of premise on. I appreciate your patience.

Unfortunately, your question is based on a flawed premise. See https://en.wikipedia.org/wiki/Phugoid for a short introduction into the pitch stability of aircraft.

Hi, your question has a few ideas which aren't well explained. Maybe addressing them would help answerers. First, are you sure you aren't confusing systems to increase stability in certain scenarios (like the MCAS, a yaw dampener, etc.) with fly-by-wire control of aerodynamically unstable fighter jets?  Second, there are a lot of other possible conditions besides unpowered and powered-with-MCAS-engaged that you haven't discussed. Finally, the statement "kinda sketchy, cuz software" as written seems more like a guess than something based on industry experience or a previous incident report.

You may also find these questions helpful: https://aviation.stackexchange.com/questions/1801/how-do-fundamentally-unstable-aircraft-deal-with-the-risk-of-computer-failure https://aviation.stackexchange.com/questions/8049/are-fighter-jets-designed-to-be-so-inherently-unstable-that-a-human-cant-fly-on

Yea, I figured I was wrong somewhere, but the premise seemed logical enough to someone who doesn't understand the nuances of aerodynamics or aircraft. I've always held an assumption that aircraft are designed to just fly straight and smooth with only the thrust from the engines and the control surfaces to turn, etc. I was not fully aware that they all have perfectly reasonable flight characteristics that will need to be compensated for. Also, I'm a software developer so thinking about some of the code I've seen used for keeping me in the sky is where that aside was from.

@codyP, thanks for those super helpful links. I was looking for something along those lines but wasn't pressing the right buttons.

Just to address a misconception

alone, unpowered, the craft is not 'aerodynamically stable'.

I don't believe this is true.

Unpowered
The problem addressed by MCAS is not specifically unpowered flight but flight when the aircraft has a high angle of attack. Because of the need to mount the wider engines further forward to maintain ground clearance, there is a tendency for the engine housing to cause additional aerodynamic forces that rotate the aircraft in the pitch axis - these forces tend to push the nose up. The forces are higher than on prior 737s.

By "unpowered" you might be thinking more of electrical power than engine power. The two are usually related. However any aircraft like the 737 has multiple electric power generators, if the generators on both main engines fail, there is a Auxiliary Power Unit (APU) that can provide electrical power. If both engines and the APU fail, many aircraft have a ram air turbine (RAT) that deploys to produce hydraulic and/or electric power. If both engines, the APU and the RAT fail, there are batteries that provide enough power for minimal necessary controls for a short while, maybe of the order of 30 mins.
I don't know about the 737, but the 30-year-old A320 family of fly-by-wire aircraft has a mechanical backup mode where the pilot can control the aircraft using purely mechanical means and non-electrical instruments. In 30 years I think the closest any aircraft has come to this was a 2005 A319 incident where the cockpit went dark and I believe the pilot flew for a while without any computerised aids, they quickly restored power and continued to their destination. I know of no reason to think the 737 is more dependent on computers for stable flight.
Even without any electrical power, an aircraft like the 737 ought to be no less "aerodynamically stable" than the earliest 737.

Aerodynamically stable
It is normal for aircraft trim to be adjusted during various phases of a flight. The aircraft is still considered 'aerodynamically stable'. When commencing an unpowered glide, the pilots would likely adjust trim. This applies to almost all aircraft.
It is normal that an aircraft in flight, without manual control inputs and without automated inputs from an autopilot etc, can exhibit undesirable flight characteristics such as a phugoid cycle. An aircraft with this sort of behaviour is normally regarded as aerodynamically stable.
I have not read anything to suggest the 737 NG or MAX series are inherently unstable. Even in an unpowered glide.
So far as I know, the only aircraft that are deliberately made inherently unstable are high-agility fighter aircraft.

Maneuvering Characteristics
MCAS stands for Maneuvering Charactersitics Augmentation System. From what I've read, a large part of the motivation for it was to make the aircraft controls feel the same as an older generation 737 - hence the name. Boeing felt that a pilot getting out of an older 737 could get into a 737-MAX and use & experience the same forces on the control yoke as before when climbing out after take off etc.

Related:

How are fly-by-wire airliners controlled in case of complete electrical failure?

Can large airliners such as a 747 maneuver without electricity?

What went wrong inside Boeing's cockpit?, BBC, 17 May 2019

It’s not quite true that the increased engine power requires MCAS. It’s the different engine geometry that requires it. Due to the engine being further forward, at high angles of attack the nacelle acts like “an extra wing”, providing lift and with it a moment pitching the nose up. This is what MCAS  counters (regardless of thrust), not the thrust-pitch-coupling.

@CptReynolds: Ah I misremembered, I'll correct my answer. Thanks.

No the software was used to fix a specific characteristic that was problematic if left to natural behaviour in a specific configuration and flight regime. If was a cheaper fix then the alternative, significant redesign with material implications for the physical aircraft.
But in itself this is not such a big deal because all sorts of airliners you are flying in today are totally dependent on software, not just partially dependent like the MAX.  So if you want to freak out over software, ride in any of the newer fly-by-wire Airbuses, or the 787.
What seems to have happened here is a typical case of a failure to cover every possible eventuality in how this particular software based solution was applied.  We live in an imperfect world, still.  The alternative is to stay home and watch TV.

I see, thanks for your answer. This was basically what I was looking for but don't know any pilots or aircraft engineers to ask.

It should be added that (unlike the Airbuses or the 787), the Max is perfectly capable of being flown without the MCAS software in question, as long as the crew stay vigilant enough to fly normal speeds. On the Airbuses or 787, more software is required for them to fly nicely, but then again the level of redundancy and fault tolerance is much higher on their software than on that particular 737 Max MCAS function everyone is keenly aware of now.

It should be noted that aircraft produced by Airbus can be controlled by pilots even when both engines fail and when the auxiliary power unit fails. They can also be flown in what is known as "direct law" with software safeguards, such as stall-prevention, disabled.

@RedGrittyBrick True. You still need the computers to run to get direct law, though. On the 737, you don’t need any computers AFAIK.

@CptReynolds: Sure but there is also mechanical backup - https://aviation.stackexchange.com/q/20963/1289

@RedGrittyBrick Of course. That’s definitely not nice handling anymore, though...


text:
Transonic buffet - reason for a rapid movements of the shockwave along the wing chord line?
I know that transonic aerodynamic buffet is caused by the separated turbulent boundary layer striking the airframe (horizontal stabilizer, wings, fuselage) with considerable force causing a high amplitude vibration, which physically shakes the whole aircraft. And during a buffet, a shockwave will be apparently moving back and forth just like in the video link I provided below:

Since the shockwave is usually stationary on the airfoil, then why it starts suddenly oscillating once we enter a buffet boundary? Any ideas?

I just wanted to ask the same question. In my textbook it says "we assume that a pressure disturbance upstream of the shock on the upper surface causes the shock to move more forward". So perhaps any kind of natural pressure disturbance present in the atmosphere will cause this kind of oscillation? I don't know.

@ymb1 Thanks I will look it up :)

Very little about air or water is "usually stationary",  it will move until forces are in balance.  The video, based on observations of the trailing edge, could also be the result of oscillations in pitch caused by the buffet.

Viewing the airfoil as a rotating cylinder, the highest velocity on it's surface occurs at the top of the cylinder (90° using polar coordinates) therefore that's where the shockwave begins and hence where flow separation will start
I know that as the free stream velocity gets higher the point at which the velocity on the surface on the airfoil (cylinder) goes supersonic occurs closer and closer to the leading edge therefore the first tendency of the shockwave is to move "forwards" (towards 0° on the cylinder representation)
I also know that flow separation occurs under an adverse pressure gradient however between 90° and 0° the pressure gradient on a cylinder is favourable (due to geometry), therefore perhaps that is why the flow reattaches when the shockwaves moves <90°

An approach to understanding this would be to try to create it.  Also helpful would be research on how to avoid it.  Aircraft routinely break the sonic barrier these days, using power to move through the "barrier" with little risk of damage.  Earlier aircraft, lacking the knowledge of "area rule" and effect of shock waves on control surfaces, in addition to less power, had more difficulty.  The keys: proper design and sufficient power.  Avoid staying in transsonic speeds.  Either above or below.
Now to understand the phenomena.  Air, like water, can absorb energy in waves.  Waves
can harmonicly reinforce one another and combine into a larger wave.  What may be happening in the video is that oscillations in the shock wave front, under certain conditions,
will combine into a larger wave and move back and forth over the wing.
Possible cures for this behavior would be to change to configuration of the wing.  Here a wealth of information exists.  My first pick would be the delta, as it's strong vortex flow might
tend to break up an oscillation.  Other wing types or modifications such as dog tooth and turbulators could be tried.
But the best solution may be not to hang around transsonic too long.


text:
What are MTRs used for?
Ok, before you say, "Military Training Routes are used for... uhh... military training," let me elaborate.
I've read about how they work with ATC and speed restrictions etc. What I'm wondering is what they do on them.
Take, for instance, IR-504. It starts in the middle of nowhere about 20 miles south of the BUM vortac in western Missouri, almost 70 miles from the nearest Air Force Base. It takes numerous turns and meanders, seemingly randomly all over northeastern Kansas. It finally ends in an MOA in the middle of the state, but once again, not by a base or anything.
I can't see any rhyme or reason to the routing and can't imagine what it would be used to train for. It's not bombing practice; only a very small section is inside an MOA. It can't be terrain following exercises; its an IFR route and 3 digits means over 1500ft agl. Besides, what terrain could they be following? We're talking about central Kansas here.
What in the world do they use these routes for?

I think they use them as a source of checkride questions :-)

Could we add a map? I have no idea what we are talking about.

@mins very good find! That makes it pretty clear. I have no idea what terrain they could be following on that particular mtr. If one knows only one fact about Kansas they know it is terribly flat. 2/3 of the state was under a prehistoric shallow inland sea. Once you get west of Lawrence there's nothing but endless cornfields

@mins To give you an idea, this is what we call a mountain

When the highest point in the county is a highway overpass, you know you're in Kansas.

@mins, if you make an answer out of that, you'll probably get the tickey mark

There is a description of this route page 1-139 of "Area Planning, MTR".

The scan is not good, you may get the textual content here too.
It says terrain following activities may take place, as well as visual contours (which I assume to be navigating without radar, looking at the outdoor and searching in a catalog the same relief contour to know where you are). As you commented, taking into account the local relief:

For terrain following should be for newbies.
For visual contours navigation should be for top-guns only.

There are different routes like this, starting from nowhere and ending in the Smoky MOA. They seem to be routes avoiding nearby airfields. On the image below, I've emphasized the area without airfields, including MOAs. It looks like IR-504 is drawn along the centerline.

Based on VFRMAP
Other possible selection criteria:

Unpopulated areas (noise from low flying jets)
Low radio noise areas.
Flat terrain for UAV training.

MTRs are used for all types of military training at low altitude.  Low altitude flying in the military is typically defined as below 5k AGL although certain systems such as terrain following can be defined slightly differently. Flying below 5k AGL with tactical maneuvering (formation, practicing weapons deliveries, or using a system like terrain following) involves a different level of focus and training than above 5k.
In your example when bringing a brand new pilot and teaching him how to trust and when not to trust the terrain following system at night at 500' and 500kts, flat is the perfect training environment. Later on I would take a student in the mountains and further build confidence in the system.
The best thing to know as a GA pilot is that the military is flying fast and often doing high-G maneuvering at low altitude so it's best to stay 5nm either side of one of these routes and fly above it by around 3-5k AGL or the limits of the original route.


text:
Why doesn't civil navigation equipment support TACAN?
Now even handheld aviation radios have GPS, VOR and ILS! I wonder why modern LCD screens with radios and navigation doesn't have TACAN? Is it coded, not useful, not certified or not used anymore? I don't think there is a problem to implement the electronics nowadays.

Why would you want it when you have GPS, GLONASS and Galileo available?

Yes, But still a lot of aircraft have VOR/DME, ILS and NDB sometimes.

So with all of that equipment, why bother adding TACAN on top of all that? More cost, and no capability beyond what you have with VOR + DME, unless you're going into military airfields. At which point, with the RNAV capabilities available today, you're probably just as well off just RNAV/GPS approaches.

@Andrius: But most aircraft (GA, at least) had their VORs &c installed decades before GPS was available.  I think I still have the original vacuum tube one from my Cherokee in the shed, and that was replaced with the current transistorized one before civilian GPS became available.  Why spend money to fix something that works?  (Especally when most of the time I navigate by looking out of the window :-))

Civilian aircraft can use part of TACAN, the Distance Measuring Equipment (DME) signal is the same as civilian DME. As for the directional component one big reason is that the military don't want you to.
Even if the military didn't mind there would likely be no demand as the costs of using TACANs outweigh the benefits. TACAN is essentially a more accurate version of VOR, and although the complexity and weight of the system has reduced the antenna is still apparently 100 pounds (45kg). For light aircraft that's a fair chunk of useful weight taken off. Cost-wise a VOR setup will set you back somewhere around \$6000 just for the equipment, call it closer to $8000 installed (roughly). A TACAN is a more sophisticated system which would cost a great deal more, say finger in the air of \$20,000, maybe more. TACAN antennas would need to be certified for every single airplane model, and that's going to add to the costs.
So for a light aircraft I'm going to lose usable weight to an antenna that is also going to throw off my weight and balance, and that's going to cost me at least \$20k when all the equipment, installation and recertification costs are factored in. That's big cash when I already have VOR, ILS, DME, NDB and 3+ satellite navigation systems already available. Oh, and I can also call up ATC most places and say 'help!' if it all goes wrong. There's just no benefit. My phone can tell me where I am if every system on the airplane fails as it has a built in GPS!
For commercial large airplanes it's the same situation. In addition to all the above most will have redundant inertial navigation systems, so even less need for it.

The antenna cannot weight 45 kg, it has nothing special, apart it is UHF, and is not directional. Here is a Collins complete Tacan "receiver" (actually a transceiver) with its antenna.

If there's so many downsides, why does the military use TACAN at all? It seems like "The military only wants to serve TACAN to their aircraft" is the real reason.

The military uses TACAN for 3 reasons:  1. The ground station antennas are gimbal mounted and can be installed on ships which would be impossible for a VOR station.  2.  When they set up a bare base airfield, they can fly in a mobile TACAN  station and set it up in a matter of hours.  3. TACAN also has an air-to-air mode to support aircraft rendezvous.  None of these capabilities are needed by civil users.  The FAA decided VOR and VOR/DME was cheaper and met all the needs of civil aviation.

Let's clarify some areas
TACAN provides both distance and bearing information. The system is interrogated and the reply is pulse coded, meaning information is delivered by the TACAN ground beacon upon request from the airborne interrogator, and not permanently. This is valid both for distance and bearing.

TACAN pulses are identical to the pulse of the civil DME system.
TACAN may deliver bearing information permanently by sending dummy reply pulses (at a constant rate of 2,700 pairs of pulses per second, adding squitter pulses if necessary to fill the blanks when not interrogated).

TACAN is often collocated with a VOR, so that civil aviation can use the DME, and military can use the VOR. The resulting equipment is named VORTAC. The TACAN can be down for maintenance or tactical imperatives.

The DME system is a civil system at the origin, and the DME function of a VORTAC is likely managed (calibrated, maintained, powered down...) under a joint agreement between civil and military authorities.

TACAN uses upper UHF band while VOR uses VHF. Back in 50s and 60s, UHF components where expensive for limited performance:

Less powerful than VHF components for emitter amplifiers.
UHF components had a lot more noise and a lower SNR than VHF, preventing affordable high performance receivers.

Today the advantage is for UHF, with equipment being more compact and allowing better performance.
Why two systems?
The divergence between VOR-DME and TACAN results from some competition between civil and NATO authorities at the time the TACAN was designed:

The civilian authorities couldn't wait for the TACAN to be operational for use in new airways.
It seems NATO agreed to use the VOR-DME while at the same time agreeing at international level to use a different system without making this decision public. See Flying Magazine, June 1955.

Size matters
A TACAN ground beacon is compact, it can be easily installed on ships, high altitude sites, and temporary landing sites. VOR-DME cannot do that due to the large radius of the antenna phased array (at least today with Doppler VOR).
TACAN compact station:

AS-4502/T instantaneous All-Band TACAN ground beacon, from ONUR
VORTAC regular size:

German VORTAC TGO near Aichtal, Source
On the image above, the low white antennas are the VOR circular phased array and the white cylinder at the top is the TACAN radome with the DME aerial at the top).
Airborne equipments are similar for VOR and TACAN, except an aircraft with both VOR and DME needs two set of antennas and two radio equipment, one for VHF, one for UHF:

TCN-550 complete airborne equipment to use a TACAN ground station, from Rockwell Collins
Differences between VOR-DME and TACAN

A TACAN ground beacon can be used for precision approach lateral guidance, due to the higher precision of the bearing information. A well known use was for STS Orbiter landing (3 TACAN onboard). Precision landing is not possible with VOR lateral guidance, an ILS must be used.
VOR can be used to transmit voice messages when a communication failure occurs with an aircraft. ATC will try to transmit messages using the VOR audio modulation (used to transmit the VOR ID). TACAN has no audio capability, the system works with DME pulses, including for bearing information.
A TACAN ground station is a transponder, and as such limits the number of interrogators, due to jamming occurring after some threshold, which may be around 200 interrogators.

Clearly both systems could be used by civilians and military, with some limitations for one user or the other:

Compactness: Military would be prevented to use VOR on small platforms like ships. Probably a no-go for military.
Control: TACAN needs to be under the control of military authorities, meaning maintenance and shutdown not managed by civilians. Likely a big problem for civil authorities.
Audio feature of VOR not available to civilians as an emergency channel.
User number limit of TACAN could be a problem for civil navigation.

Civil authorities not using TACAN
Reasons include:

Early competition with military and military delaying agreement.
Control over ground stations.
Unlimited number of users for VOR (still limited for DME).
Easier maintenance.
Voice capability.

Why would the military need to be in control of all TACAN stations?  Why couldn't you have at least some civilian-managed TACAN stations?

@Sean: In a world with fully civilian TACAN stations, this would be possible (TACAN is used mostly for landing by military, not for enroute navigation)

FYI
TACAN ground stations maintained by the FAA are in use every day.  When a TACAN ground station is collocated with a VOR beacon, it is referred to as a VOR/TAC station vs. a collocated VOR/DME station.  Check your charts.
The TACAN station produces signals in response to the TACAN interrogation to determine range (by time measurement from the aircraft interrogation to the time of response receipt at the aircraft) and receives phase shifted signals to determine azimuth (bearing), whereas the (L-Band frequency) DME only produces range and the VOR operating at a different (VHF) frequency produced range.
The reason for TACAN is on a military situation is that the TACAN station may be portable.  It can be trucked, air dropped, or in hardship cases man-packed into a specific point for military aircraft enroute navigation or approach by a fixed-wing or rotorcraft to a temporary landing site.


text:
What is the permissible deviation for a pilot to stop the aircraft when guided by AVDGS?
As per ICAO Annex 14, table 5-4, the permissible deviation for AVDGS is 500mm at stop position, which is the design requirement for AVDGS unit.  I would like to know what is the permissible deviation for the pilot to stop the aircraft when guided by AVDGS, specifically, how far he is permitted to go after the stop signal?


text:
Where is the fire suppression material injected into a jet engine?
This question is regarding the P&W 4000 engine that was involved in the recent incident on UAL 328, but it doesn’t have to be specific to that engine.
From what I gather in this incident the fire continued after both fire suppression bottles had been deployed. I’m wondering where exactly does the suppression material go into the engine? Does it all flow into the core or is it distributed to different places. Does the loss of the cowl render it ineffective? I expect that halon would only work in an enclosed space. It appears that the fire in this incident was outside the core and without the cowl there wouldn’t be much that could be done in flight to put it out.

Related: How does a fire suppression system work?

I’m wondering where exactly does the suppression material go into the engine? Does it all flow into the core or is it distributed to different places.

It is distributed with some nozzles. But the exact position of them depends on the specific engine. In this slides you can get an idea of the positions for a turboprop engine. They usually cover at least the core, and some other zones that should be separated by firewalls. This image (from Boeing) gives you an idea of the different zones, which I expect they are covered by different nozzles:

and this image (from the same link) contains the position of the fire detectors, which I expect to be covered by at least one nozzle:

Does the loss of the cowl render it ineffective? I expect that halon would only work in an enclosed space. It

Probably yes. Engines are not designed to have catastrophic failures like the Flight UA-328 (they are supposed to contain any failure). So, probably not even the fire protection system is designed to handle such case. A large destruction like that may have potentially cut some of the fire protection tubes and damaged the firewall protections.


text:
Is there a minimum distance between a runway and a public road?
Does the FAA require a minimum distance the between the TDZ of a runway and a public road?
The reason I ask is because an aircraft landing at a small GA airport (Garnett Municipal, K68) came across the roadway I was driving on low enough that if I'd been 200 yards up the road he'd have hit my truck. Or at least he'd have had to go around.

From the satellite pic you can see that the end of the runway is about 30 feet from the road. The TDZ is about 150 feet. A 3° approach would put you just short of 8' AGL at the road, which is just about exactly how high he was. My truck has a clearance of 10', so it's quite possible to strike vehicles on the road if one is too focused on the runway.
Although it's not a highway (that's about 1000' from the runway), it's the only paved road going east/west for several miles so it gets a bit of traffic
Is it common to put a runway so close to a road?

No, in fact there are public roads so close that they caution drivers to stop and listen, there is a pretty famous accident that a student pilot had during first solo. As a side note, he did quit flying at first but then went on to finish his ticket. You can read the NTSB report here

Just missed my edit window, what I meant was that it isn't uncommon to have a road that close, although public use airports have to be built to some standards (the video I posted is a private airport). I'm trying to locate that standard for you and I'll post an answer when I find it.

I think the answer is in AC 150-5300-13A Section 308 the "Obstacle Free Zone", although you have to be a civil engineer to understand it.

Internationally, there are some great counterexamples. Gibraltar, for  instance, where the only road in runs across the runway (they do have officials that close the road for aircraft movements).

It's not as bad in the image you posted. The thing is that the runway only starts with the thick white line.

As Jan says, the actual runway in the picture is more like 150-200 feet from the road.

@JanHudec I based the numbers in my question.on the white line. 3° at 150' is about 8'. I'd never seen anyone come in quite so low so I was wondering if the approach was abnormal but it appears that it was textbook.

@TomMcW, but the aiming point is not at the beginning of the runway. On long runways it is 1000' past the threshold, but it obviously needs to be closer on short ones.

@RonBeyer - Yikes!!!!  @ mins - yikes!!!

@JanHudec The runway length at K68 is 2660' which is plenty for many small aircraft but it isn't huge so I think many pilots would probably use the numbers as the aiming point. You might even flare over the arrows if you needed all the runway length you could get.

One thing worth noting is that even where there are laws, rules, or regulations, they often do not apply retrospectively. eg where an airfield was built before the law came into place, there is not always a requirement to update it

@Pondlife The other explanation is that they were practicing short-fields, when I did short fields with my instructor if I didn't put it down on the runway threshold lines I had to go around. My DPE was also pretty strict about that.

Either way, just with my common sense, the road could use WATCH FOR INCOMING AIRCRAFT FROM LEFT/RIGHT signs.

Yes, there is a minimum area that must be free of obstructions and closed to vehicles, but only for airports that have air carrier operations (see 14 CFR 139.309) or that receive FAA grants. AC 150/5300-13A - Airport Design has all the technical details; the actual distances are calculated from formulas, so there's no single answer. If you're really curious, you can read all the gory details in Chapter 3 and this FAA FAQ has a (very) simplified explanation:

What is the size of the RSA [Runway Safety Area]?
The RSA is a rectangular box surrounding
  the runway and is based on the runway design code. The dimensions
  range from 120 feet to 500 feet in width and 240 feet to 1000 feet in
  length beyond the departure end of the runway. (see FAA Advisory
  Circular 150/5300-13, Airport Design) Generally, on airports that
  serve air carrier aircraft, the RSA extends 250 feet either side of
  the runway centerline and 1000 feet beyond each end of the runway.

You didn't mention which airport you're asking about, but presumably it's either privately owned and/or doesn't receive FAA grant money.

It's K68. Very small, one runway, non-towered airport owned by the city of Garnett, KS. I have no idea about funding. I've seen that beach in St Maarten on tv. That's pretty wild. I'd love to see that in person some day

No (for smaller airplanes and airfields)
The limit is not regarding the runway to the road but the minimum height an airplane (landing or starting) has to have over the road.
You can see this very well in the picture:
A departing aircraft (runway 19) can be quite close to the road and use the "full" length of the runway as it is built. As long as the thrust is not too big (for smaller airplanes), there is no reason for a restriction.
A landing aircraft (runway 19) requires a minimum height (15 feet i think) and is therefore not allowed to land at the beginning of the runway but not before the big, white bar. This is called a displaced threshold. So the runway, for landing aircrafts, actually does not begin so close to the road as it "looks" like.
This way, departing aircrafts will have a longer runway available, which is a critical point in aviation (safety).
It's btw the same for a departing aircraft with direction to the road (so using runway 19 + 18 = 37 => runway 01). It is not allowed to lift off after the displaced threshold.

The FAA regulates aviation and aircraft, not road layout or runway locations.
The standard glideslope is three degrees, pretty shallow, so aircraft often travel long distances low above the ground prior to landing. Trees are a big issue. On the island of St. Maarten 747's fly as low as 10-15 feet right over a heavily populated resort beach and pathway.

Credit: Blick, William E. Princess Juliana International Airport
Often there are signs warning of low-flying aircraft so that motorists are not startled.
Don't worry about it too much, planes are way more flimsy than a truck, so as long as the 50 gallons of aviation fuel does not catch on fire or explode, your vehicle will come off much better in the rare event of a collision.

There's pretty good visibility there, so I'm sure they would see something coming... as long as they are paying attention. I can imagine a new pilot being focused on the landing, airspeed, configuration, etc and forgetting completely about road traffic. It just totally surprised me seeing how low he came over the road. I was watching a couple of crop dusters taking off and landing there yesterday and they were quite a bit higher than this plane was. But those crop dusting planes are really agile and powerful so they obviously don't need the whole runway. They have have an amazing climb rate.

Do you have a citation for your claim that aircraft cross the beach at Sint Maarten at 10-15ft AGL? The photo looks much more like 30-40ft and crossing the beach at 10ft would surely result in clipping the airport fence.

Also, please acknowledge the source of the image.

@Richerby The fence is 8 feet high I think and the planes come right down over that fence. There is a roadway or pedestrian way right next to the fence. You can't see the fence in this photo. I was talking about the altitude near the fence.

Totally OT, but I can see hanging out on that beach for a few landings as a novelty, but it certainly doesn't look like a relaxing vacation destination for spending the whole day...

@FreeMan Spread out your towel, put up your umbrella, put on your suntan lotion, then put on your hearing protection headcans!

@TomMcW - that's what I said, not a very relaxing location for the day.  :) /OT wandering...

Princess Juliana looks like a disaster waiting to happen - just imagine if a plane came down short of the runway...


text:
Are monoplane struts under tension, doubling the stress limit of the spar?
Are monoplane struts under tension, doubling the stress limit of the spar?
If monoplane struts are under tension, they would be pulling the wing down,
which would put the bottom of the spar under compression, at least between the strut and wing root where the load is the highest.
However, the aerodynamic load when flying is upwards, trying to bend the wing up, so the bottom of spar would have to go from 1/4 max compression ultimate stress, through zero and all the way to 1/4 max tension ultimate stress to reach 1/4 max flying stress limit. Assuming both limits are the same and the safety factor, n is +/-4, hence 1/4 max ultimate stress.
That would roughly double the amount of stress the spar is allowed to  carry.
Sort of like prestressed concrete.
Is this correct?, at least conceptually?

You should add a quick drawing to better describe your understanding. You may indicate on it where the forces you are talking about apply. It may be quite easier for us to understand your comprehension of the phenomena and have a more precise answer.

The spar on a strut braced wing effectively moves the bending stress out from the wing root to the strut attachment.  In other words, a strut braced wing is a cantilever wing from the strut attachment out, and will have the normal bottom cap in tension and upper cap in compression at that point.
Between the strut and fuselage, it's more complicated.  The spar along that section is like an inverted hammock being effectively supported at both ends.  It wants to bow up. At the root fitting, there are shear forces which depend on how far out the strut attachment is.  The forces are inboard and up if the strut attachment is closer to the tip, and inboard and down if the strut attachment is closer to the root (a Twin Otter's wing's root fittings are under inboard and downward shear because most of the wing is outboard of the strut attachment).  There is a 'sweet spot' point where you can attach the strut to the wing spar and the loads on the root fitting are straight-in compression with no vertical shear.
This is why you will see astonishingly small bolts attaching the wing root to the fuselage on some airplanes (as in, half inch, or 5/8 inch diameter bolts at the strut attachments, and quarter inch bolts at the wing roots); if the strut picks up the wing at the right location, the loads at the root are almost all very moderate inboard shear loads.
As far as spar bending goes, the most highly stressed location is the cap strip above and below the outer strut attachment and that is where the spar has to be strongest in bending, with tension loads on the bottom and compression loads on top, in normal upright flight.

Omg this brings back some very bad memories from the uni statics course :)


text:
Why don't rudders stall at 30 deg deflection, as they don't have downwash to reduce local AOA like flaps and horizontal tails do?
Why don't rudders stall at 30 deg deflection, as they don't have downwash to reduce local AOA like flaps and horizontal tails do?
or do they?
I understand flaps and horizontal tails don't stall at 30 deg deflection as the downwash from the wing reduces the local Angle of Attack, so flaps and horizontal tails aren't seeing an angle of attack
 of 30 deg even though they are deflected by 30 deg.
However, there is no "vertical downwash" from the wing to help the rudder.  Why don't rudders stall at 30 deg deflection when most classic NACA airfoils stall at about 15-20 deg?

It's just a wing sticking up, so there is a "sidewash" no?  Same thing pretty much.

@Fred - Are you sure they don't?

Are you talking about an all-moving vertical tail? Otherwise I don't see what AOA has to do with rudder deflection.

Why do you expect a trailing edge surface deflection to be comparable to the deflection of the entire airfoil?

@RobertDiGiovanni not my point; a $30^o$ deflection of an aileron will not increase the $\alpha$ of the entire airfoil by anywhere near $30^o$, more like $15^o$ if the aileron takes about half the chord (for small angles, etc).

What folks need to understand (before hysterically downvoting) is the mechanism of "rudder stall" (why they added the fillets to the P51).  In order to stall the rudder, you must increase AOA FASTER THAN PLANE YAWS.  What you wind up stalling IS THE OPPOSITE SIDE OF THE FUSELAGE, HENCE MUCH DRAG.  This is why slipping makes a lot of drag.  AOA of TAIL DECREASES as plane YAWS.

@RobertDiGiovanni I don't think anybody fails to understand that yaw mitigates the $\alpha$ seen by the VTP. But that has little to do with OPs question which, unless I am confused, can be summed up as "if an airfoil stalls at $x$ degrees, why can I deflect a flap/aileron/rudder to $2x$ degrees without stalling?"

@AEhere good point, we must remember to draw the chord line from the leading to trailing edge, which INCLUDES the control surface.

Deflect the rudder relative to the vertical tail and there will be sideslip $\beta$. In the situation in the drawing: deflect the rudder to the left, and it will be in line with $\beta$ but will have a deflection relative to the vertical tail.
So you may deflect the rudder 30° relative to the vertical tail, have for instance a 12° side slip angle as a result, and have an 18° angle relative to the free stream.
Note that the drawing depicts induced side slip flow at the vertical tail as well.

+1 for showing (wing tip like) airflow created by the FUSELAGE AOA to the free stream.  But notice the plane must be yawed for this to occur.  The greatest danger of rudder stall is the initial, sharp application.  Even stalled, it will still yaw the plane.  But another plane (like the Stearman) with a delta-like Vstab/rudder, will "snap" faster, giving it an advantage.

At an extreme deflection (like 30º) a rudder is probably stalled. But in that condition, lift does not entirely disappear, and drag increases a lot. The resultant of the two forces (the 'aerodynamic force') pushes the tail sideways, yawing the airplane. Hence, that stall doesn't matter much...

I believe the vertical stabilizer don't create lift been in line with airflow,so if stall is short term because the max. deflection is short time (then no feeling of stall).


text:
How to choose an angle of incidence?
How to choose an angle of incidence?
Looking at typical airfoil polars, it seems most classic NACA GA wing airfoils like the NACA2415, have similar properties:

A max Cl/Cd at about 5-7deg
Lowest drag on the drag polar between -5 and +5 deg, then drag increases substantially outside of this range.
0 Cm at about 10-15 deg.

Interestingly, these ranges don't really overlap.
Also, I understand for maximum efficiency, we should design a plane
to cruise at 0 moment.
So ...do we choose the angle of incidence with the lowest drag, or the highest Cl/Cd, , or 0 Cm and then adjust airplane geometry for a CMplane of 0 at cruise?
Based on the above data, my intuition says to:
determine the cl needed for Vcruise, determine the AOA needed to generate that lift on the lift curve, and check that that angle of incidence is about 2deg, near the highest Cl/Cd vs Alpha at 5-7 deg, which still gives me a bit of leeway before the drag really increases past +5 deg, , and then adjust airplane geometry to get a CMplane of 0 at my chosen Vc.
Is this correct?


text:
What would happen if ultralights had mountain bike style treaded tires?
What would happen if ultralights had off road treaded tires?
Mountain bike tires are made for going off road through mud, etc.  They have voids between the tire lugs to clear mud etc.
Why not off road going airplanes?
I assume the reason is, the lugs would catch air and start the tire spinning during flight?
Is this correct?
Or is it just a drag thing?

For posterity, lugs are the "knobs" or "bumps" sticking out from a tire, which make up the part of the tire which contacts the ground. (When I did a Google search for 'tire lugs,' initially Google just told me about lug nuts, which are unrelated to the lugs mentioned in the question.)

Not sure what type of tires are currently used on an ultralight, but my hunch is that your typical MTB tire is larger in diameter and heavier than what you'd want for your ultralight. Even very light competition MTB tires/rims.

"Ultralight" is an ambiguous term. It's a very different thing in the US compared to the rest of the world. I doubt mountain bike tires would handle the forces of a half ton aircraft landing at 50-ish knots, so that's probably not what you're referring to, but you might still want to clarify what variation of "ultralight" you're referring to.

Fair enough. Actually my question was just about aggressive treads vs smooth tires

Consider the difference between a tire used as part of a propulsion system and a tire not used as part of a propulsion system.  Consider the difference between a tire used as a part of a steering system and a tire not used as part of a steering system.

Mountain bike tread is meant to sink into the mud in an attempt to gain traction on firmer ground beneath the mud.  A plane generally doesn't want to sink into the ground (even during braking), if it sinks too far during landing or take-off, the airplane is more likely to catch the forward gear and flip/strike the prop.
Bush plane tires are designed to land on soft fields.  The difference between mountain bike tires and bush plane tires is that the high surface area of the bush plane tires attempt to "float" on top of the soft ground rather than dig into it:

Excellent point.

So....If you did use a mountain bike treaded tire, would it start spinning during flight?

If the tread is non-reversible, I'd imagine they could due to the small amount of asymmetric drag.  I've got Continental der Barons on my MTB, the one side of the tread is chamfered while the other isn't, the top of the tire would produce more drag than the bottom.  Would also depend on the wheel bearing.  The larger the aircraft, the heavier-duty the bearings and the higher the bearing rolling resistance

@Fred: It's quite normal for light aircraft tires to spin during flight.  Doesn't hurt anything.  WRT treaded tires, you want the least amount of friction practicable for takeoffs, and as much flotation as possible for soft fields.  AFAIK, the only reasons for tread grooves in airplane tires are 1) to prevent hydroplaning on wet runways; and 2) as a wear indicator.

@Fred very likely yes.  Although there's a good chance the wheels will rotate backward due to the proximity of cabin and wings causing different airflows above vs below tyres.  Additionally there would be more drag while in flight, assuming fixed gear.

It's mostly the tendency of the lugs to throw up dirt and mud, and the fact that most of the time you aren't doing the hard braking in soft ground that would make tread lugs worth having, so it's really no point unless you really want soft ground traction for braking and are willing to live with your tires coating the bottom of the wings with crud all time.  Most ultralights stop pretty quickly when they land anyway and don't really need heavy braking ability on soft terrain.
Big airplanes in the 30s and 40s commonly used diamond tread tires because they still operated from grass a lot, but that practice faded as soon as paved runways became the norm.
If your ultralight is a taildragger with good brakes and lugged tires, you'll end up with too much braking traction and nose it over, so it needs to be a trigear if you want to be able to do that.  I think you'd find in the end that 90% of the time, having lugged tires or regular ones makes very little difference overall if you are only landing at 25 mph in the first place.

Hmmm-- related question-- what was the tread on the tires of the Spirit of St Louis (Ryan NYP)  -- Lindbergh carried mud from New York on the bottom of his wings all the way to Paris.

Tires of the time typically used a diamond tread pattern.


text:
Do Alaskan bush pilots generate a Clmax of 5 with 90° flaps?
I understand the Alaskan bush pilots use 90° flaps in the Valdez STOL competition. I think this would stall the flaps. And if so, it wouldn't increase lift and reduce stall speed, but Javafoil says the opposite.
Perhaps this is more for lift/lower stall speed than drag. Since they land flat halfway down a long runway they don't need drag to slow down.
Just to do a test, I input a NACA 2415 foil in javafoil, 25% chord flap, 90 deg flaps deflection. And as expected, lots of drag, but Clmax jumps from 1.5 to 5 at about 0 deg AOA.
Is this realistic? If not, what is the real Clmax?

A STOL landing is typically best accomplished at high drag with power on. This is especially true of aircraft with a high power to weight ratio, as is typically the case in these competitions. The STOL landing technique will typically involve a higher than normal (e.g., greater than 3°) descent angle with a touchdown near, or even beyond, wing stall. Thus, the greater drag of greater flap extension likely aids in maximizing the short landing performance.

They actually land pretty flat WITH POWER OFF in this competition as it is in halfway down a runway and not a clearing surrounded by trees. It's really a test of short landing roll, rather than a typical STOL landing with a short approach and short landing.

To be clear; while this behaviour is most common amongst Alaskan bush pilots, other bush pilot subspecies around North America have been observed to use 90* flap deflection as well. Biologists believe this is a form of territorial display.

I'd say you are seeing oddball numbers because the effects of 90 deg flap are outside of javafoil's normal parameters.

The following graph is from Cahill, Summary of Section Data on Trailing-Edge High-Lift Devices. As you can see, for a plain flap, with gaps fully sealed, the $C_{L_{max}}$ maxes out at around 60deg.

When I played around with xfoil, things became unreasonable beyond 40deg. Probably some assumptions in the boundary-layer equations broke down. Since Javafoil utilizes the same computational approach as xfoil, I would expect the same behavior.
On the Alaskan Bush pilots, are we sure they are 90deg deflection, and not just some high deflection that looks almost vertical? With multi-element, slotted flaps, you can do better than plain flaps.


text:
Why is the delta wing naturally stable in pitch?
Any thoughts on why the delta wings are naturally more stable in pitch, so they don't require any tail surface? What's the physics behind this?

"What's the physics behind this problem?" Problem? Why is this a problem?

Never seen a Flying Plank?  Rectangular wing with a vertical tail and cockpit pod.  Very stable in pitch.  Neither taper nor sweep.

@ZeissIkon whether or not Darjan has seen a Flying Plank, the issue remains as unclear as before your comment. He's asking about the physics and what makes it inherently stable, not what delta planes exhibit such characteristics.

This is a very good question, as it shows some of the misunderstandings regarding "tailless" aircraft.  With deltas, one can consider them as blended wing/tails.
The function of a horizontal tail surface is pitch control.  The back of a delta is certainly large enough to do this. So much so, that now one can design
a forward canard to go with it.  This plane should pass the horizontal drop test (nose must go down).
Notice that birds, wanting more straight wing lift,
"unblend" a little and also have a fan tail.  Delta's do not generate as much lift as a comparable straight wing.
So designers can work with what they need, particularly with desired speed range.  Faster, the wings can pull in a little, as with the FB-111 swing wing.


text:
Can a pilot act as cabin crew member?
If several standby cabin crew members called in sick and there are no more available can standby pilot called to perform cabin crew member duties? Probably it would be more economical than postpone flight let say with 200 passengers...

it could be jurisdiction-dependent. are you interested in a specific one? (faa? easa?)

I'm not sure if this is possible. Cabin crew are trained for a number of things including handling of emergency situations, which are different from what the flight crew receives. Also, there is no reason to believe that the flight crew is proficient in various duties of the cabin crew (like performing safety demonstration, etc) as their duties are distinct.
On the regulation side, the certification requirements are different. For example, the FAA requires the cabin crew to have a certificate of demonstrated proficiency.

In the fall of 2003, Congress established a flight attendant certification requirement in the Vision 100-Century of Aviation Reauthorization Act.
The act requires that after December 11, 2004, no person may serve as a flight attendant aboard an aircraft of an air carrier unless that person holds a certificate of Demonstrated Proficiency (certificate) issued by the FAA.

This would mean that the flight crew can't operate as cabin crew (unless they have the certificate), atleast in US.

The Answer for your question is NO.Pilots are not trained to serve passengers, but I think that was not What you were referring.  Pilots can and must help flight attendants in emergency, this does not mean they are working as a flight attendant, in case of an emergency the pilots will finish all the emergency check lists turn off engines, APU and Battery as part of the check list procedure and after that will communicate the evacuation of the aircraft. After this command the pilots have to leave the aircraft, so in this case the pilots can help the flight attendants with the passenger evacuation. Sometimes asking the flight attendant to jump off in the scape slide and help the passengers at the other side of the slides. Remember that this is a quick procedure as a time to evacuate any commercial aircraft is 90 seconds by regulation. Hope this help ;)


text:
Why don't airplane turbo piston engines have boost control?
Why is it possible to over-boost piston aircraft engines? All turbo car engines have a wastegate that just vents pressure back to the intake, whereas in an airplane the pilot has to look at the manifold pressure gauge to protect the engine.

The majority of piston airplane engines are based on very old technology, before computerization was available. The vast majority of airplane piston engines are carbureted with manual mixture control, prop control and turbo control and the pilot has to manage all that plus carb heat manually.
New engine technology has been very slow to come into the piston market because certification costs are so high, and the market is so small. It would cost engine manufacturers millions to develop and certify new turbo-normalizing systems for these old engines and as there are probably only a few thousand turbo-normalized avgas piston airplanes in the world they would never recoup the costs.
There are modernized engines on the market with electronic fuel injection, computerized engine management with turbo-control, and single-level operation. These are slowly making inroads into the market but it's going to take time.

Some of the early, basic, turbocharged aircraft did have a manual waste gate control. "Turbo-normalizing" was designed to allow turbocharging at altitude and was not to be used a sea level. If not used properly, it would be possible to over boost the engine at low altitude but a "blow off valve" was incorporated to prevent damage to the engine.
N93641, 1973 Bellanca 17-31ATC Super Viking control panel showing manual waste gate control below throttle:

It is possible to overboost ANY turbocharged or turbo-normalized engine if handled improperly, aviation or otherwise.
Now a dedicated turbocharged engine generally uses an sutomatic waste gate to control the flow of exhaust gases through the turbo, thereby regulating the manifold pressure available to the engine.  They're also a little more ruggedly built that a normally aspirated engine specifically for that purpose.  That being said, they do have their limits and smooth throttle inputs are suggested to minimize the risk of an overboost condition below the turbo's critical altitude.
A lot of normally aspirated engines were turbo-normalized, that is fitted with an aftermarket STC turbo kit (The Bellanca above looks to have been fitted with a Rayjay STC turbo kit).  Older STC kits for turbo normalizing used manual waste gate controls which had to be adjusted manually and we're not cleared for used below 3000-4000 feet to prevent overboost.  Here pilot negligence does present an opportunity for over boosting and damaging the engine through failure to regulate the waste gate and or engage/disengage the turbo at low altitude.  There are s number of aftermarket STC turbo kits such as those made by Tornado Alley which do have automatic waste gates to reduce pilot workload such as those found on the Cirrus SR-22 Turbo and Mooney M20TN.

Why it's possible to over-boost piston aircraft engines?

It's not. Unless the system is malfunctioning or not set up properly.

while in the airplane pilot has to look at the manifold pressure gauge
  to protect the engine.

This is simply not true. A pilot only has to look at the gauge to set the manifold pressure to whatever power setting he desires.
The turbo will never over boost. All piston turbo aircraft have had over-boost protection since day one. Most often by waste gate.
They are not controlled by computer. They use pressure controllers that sense manifold pressure and divert oil pressure to supply muscle to open the waste gate.

PA-44-180T Turbo Seminole has 2 over-boost  indication lamps. If you a low and cold and apply full throttle you will two red lights in the cockpit.

I'm fairly sure the Cessna T182 has a manual wastegate system and it is possible to overboost the engine. The newer T182T has automated it, though.


text:
Is it OK to make an approach without any straight-in segment at all?
Let's say you are on a 180° heading right of the airport and want to land on runway 36. Abeam 36 you can make a descending turn left, flare and start leveling off at the same time, touch down with the left gear, level off and finish the rollout. No problem in a GA aircraft. Can this be done in an airliner, for example in a circle-to-land approach? What is the minimum straight-in segment required for circle-to-land?

If the aircraft has not established a stabilised approach, a go around is required. According to EUROCONTROL's Skybrary, a stabilised approach is defined as:

Their Approach-and-landing Accident Reduction (ALAR) Briefing Note 7-1 suggests that "all flights must be stabilised by 1000 feet above airport elevation in IMC and 500 feet above airport elevation in VMC. An approach is stabilised when all of the following criteria are met:

The aircraft is on the correct flight path
Only small changes in heading/pitch are necessary to maintain the correct flight path
The airspeed is not more than VREF + 20kts indicated speed and not less than VREF
The aircraft is in the correct landing configuration
Sink rate is no greater than 1000 feet/minute; if an approach requires a sink rate greater than 1000 feet/minute a special briefing should be conducted
Power setting is appropriate for the aircraft configuration and is not below the minimum power for the approach as defined by the operating manual
All briefings and checklists have been conducted
Specific types of approach are stabilized if they also fulfill the following:

ILS approaches must be flown within one dot of the glide-slope and localizer
a Category II or III approach must be flown within the expanded localizer band
during a circling approach wings should be level on final when the aircraft reaches 300 feet above airport elevation; and,

Unique approach conditions or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing.

An approach that becomes unstabilised below 1000 feet above airport elevation in IMC or 500 feet above airport elevation in VMC requires an immediate go-around.

(Source: www.skybrary.com)

Nice (LFMN) has RNAV approaches to 22R and 22L that are circling, to avoid a mountain range right behind the runways. Not often in use, but a very fun approach as a passenger (and flight crew, I reckon)

@JustSid -- there's also Martin State (KMTN)'s VOR/DME or TACAN RWY 15 approach, which has a DME arc for its only leg, and effectively no straight in final approach segment as a result.

The most extreme approach is probably VQPR runway 15. The aircraft wings get level around over threshold, 50 ft or less (they are level by 50 ft on this video but there was another where they were not until 30 ft).

But this is only recomendation

@JustSid: The circling approach for  rwy 22L/R has still a small straight-in segment parallel to the Promenade des Anglais. Well parallel as wind permits ;-)

By those criteria, runway 13 at Kai Tak (old VHHH) would have been unuseable for landings, due to the sharp low-altitude turn necessitated by an inconveniently-placed mountain.


text:
Stalls: which flight control surface is effective last?
In an aerodynamic stall, which flight control surface (limited to ailerons, elevators and rudder) remains effective for the longest period of time during the stalling condition? In other words, which of the three loses its effectiveness last?

It depends on the type of stall and the loading configuration of the aircraft. The short answer is that the rudder typically stalls last because the angle of attack of the wings is independent of the AOA of the vertical stabilizer. However it's usually among the least effective control surfaces in getting out of a straight dive (very useful for recovering from spins and spiral dives though).
Of the horizontal surfaces, it depends on which one has a higher AOA at the time the wings stall, which is dependent on how the plane entered the stall, and how the aircraft is configured. A sudden pitch-up in an airframe with an aft CG will cause the horizontal stabilizers and thus the elevators to depart first. In most other situations especially when the CG is forward of the CL, the wings will have the higher AOA as the nose pitches downward, so the elevators will remain useful as long as the tail isn't caught in the turbulent airflow off the wing. T-tails have this disadvantage; the higher tail location normally puts the tail in cleaner air, but in a stall the turbulent air off the wing shelters the tail making it less effective.

Standard configuaration
In a stall, the first part to show large-scale separation is the inner wing. This is intentional - all control surfaces should stay operational as long as possible. When the angle of attack is increased further, the separation extends outward and affects the ailerons first. The elevator flies in the downwash of the wing and sees less of an angle of attack change, even in an aircraft of marginal stability. With positive static stability, the lift coefficient of the horizontal tail is lower than that of the wing, increasing its stall margin further.
If the pitch-up is violent enough to even stall the horizontal tail (which happens regularly in a spin), the rudder will still see attached flow, albeit at a strong "sideslip" angle. But it will still be attached in the symmetric flow of a deep stall. In a spin, it might also separate if the rate of rotation is high enough.
So the sequence for separation in a stall is:

Ailerons
Elevator
Rudder

Canard configuration
In a canard, things are reversed between wing and elevator, and the forward wing and its elevators will stall first. This way, the aircraft will pitch down automatically. Here the sequence is:

Elevator
Ailerons
Rudder

During recovery, the sequence is reversed: The control surface which has attached flow last will also be the first to show re-attached flow.
Note that separation means that only one side of the control surface shows separated flow - the opposite side is still working and provides the pilot with a limited controllability.


text:
Is it easier to land planes on an aircraft carrier with a high flight deck?
The Wikipedia page for the USS Wolverine says that the low flight deck of that carrier is disadvantageous for warplane landing, but it was 70 years ago.
Assuming other things (including displacement, length, width and draft of carriers, flight deck length, width and texture.), is it easier to land the latest planes on an aircraft carrier with a high flight deck?

I couldn't find where the linked Wikipedia article mentions a low flight deck (only problems arising from low speed). Could you edit a quotation into your question?

Then
It used to matter, because aircraft would sometimes approach the carrier at a lower altitude than even the flight deck before pulling up briefly and practically stalling onto the deck, allowing for a lower speed landing. Similarly, the higher flight deck would give an extra couple of metres of acceleration if over-shooting the flight deck and having to go around. As such a high-decked carrier gave a little more margin for error.
Now
It makes virtually no difference - modern aircraft approach at the same angle and airspeed regardless of the height of the deck (within reason). They also perform approaches significantly more accurately. If anything, the higher deck could be considered a (very) slight disadvantage, as it may display a higher rolling moment than a low deck carrier. This is unlikely to cause any issues, however.


text:
How much does a refueling stop for an Avro RJ85 cost in Bolivia/Colombia?
One possible motive for the LaMia disaster is that they were attempting to save money by not refueling. That may or may not be true and this is not the place to debate that.
Reports say they were supposed to refuel in Cobija, Bolivia and after the delay they would have had to refuel in Bogotá. How much would a refueling stop for that airplane have cost in Cobija and/or Bogotá?

@Pondlife I am not speculating about an accident as  you pointed out. I just want to clear out one piece of information that is related to that accident. There is no opinion. The prices / fees and taxes of operating and refueling an aircraft in south america are facts, that is what I am asking about.

According to the analysis in the AvHerald article, Bogotá is already beyond the legal limit.

It's hard to give an exact figure as their are a number of considerations. If we assume that the re-fueling stop is at El Dorado, and the airplane was a BA146 (RJ85 is a variant) then approximate costs might be (in USD):

Landing fee: at about \$6 per thousand kg, and 42,000 kg would be about \$250. Add 5% for a night landing and another 5% for a night departure for about \$280
Handling charges: this is hard to say, estimate $100
Jet Fuel: the BA146 can carry up to 3000 US gallons, assume 1500 as it's a short hop, at \$3.16/gallon that's \$4740

So it would seem that about \$5000 is a good working figure. Keep in mind they wouldn't have used all that fuel to get to their destination, there would have been plenty left and they wouldn't have had to fill up completely on the way back, but the most expensive part of a flight is the climb to cruising altitude, so 2 climbs are more expensive than one. There might also be ATC fees for filing another flight plan, and taxes not listed, I would imagine that wouldn't change the costs that much - the fuel is still the big chunk of the cost.

As you say the 2 climbs would be more expensive, it would be interesting to see the fuel burn numbers for non-stop versus making the fuel stop, as this is the true additional fuel cost of making that refueling stop.

That would help to narrow down the true costs of a stop, not information I have though.

Avherald posted data for a few non-stop flight plans that seem to have a lot of detail, it may be possible to estimate from there.

Bogotá (El Dorado) is just 100 nm closer than Medellín (Rio Negro), already beyond the range (see the mentioned AvHerald article).

Bogota was definitely farther then they should have gone, but given they almost made it to Medellin they would have made it. I chose that as a refueling stop because it had information on costs that I could use to answer, not that I thought it was the best choice. I would expect other airports to be similar.


text:
Are the cockpit and crew rest area considered part of the cabin?
A few days ago, a travel blogger wrote about smoking on a China Eastern flight, and the smell of cigarettes came from either the cockpit or the crew rest area:

So I’m not sure who is smoking, though I have to assume that it’s
  either the pilots in the cockpit, or otherwise the flight attendants
  in the galleys and crew rests

The CAAC's (Civil Aviation Administration of China) decree #71 banned smoking in the cabin and toilets in domestic and regional (HK, Macau and Taiwan) scheduled flights, as well as smoking in non-smoking areas and toilets for international flights. The major Chinese airlines don't have smoking areas on international flights anyway.
In reality, many pilots and first officers on Chinese airlines smoke in the cockpit, regardless of whether it's a domestic or international flight. It seems that the cockpit and crew rest area are not part of the cabin according to Chinese standards.

Are the crew rest area and cockpit considered as part of the cabin according to ICAO?
Does any major civil aviation authority consider them to be part of the cabin?

It's possible they are ignoring the rules.

Definitions are multiple, what is pertinent here is the definition used by CAAC when publishing the decree. When the ICAO uses the wording "cabin crew" or "cabin safety", it doesn't include the flight deck. See also this Wikipedia definition. On the other hand "cabin pressure" is related to the entire volume within the pressure vessel, this includes the flight deck. That said, the blogger's unstoppable moral duty to inform might have sent the poor crews to China's jail.

They are ignoring the rules. I have heard a non-Chinese (Western) turbine Captain relate how his Chinese FO's pleaded with him on longer sectors about being able to light up. Smoking is considered socially acceptable anywhere at anytime by the Chinese, even if it is technically illegal

Speaking as an ex cabin crew with one of the world's largest airline. I can definitely say that the CRC is part of the cabin, as safety and security checks are completed by the crew as part of cabin checks.
Flight deck if I'm not mistaken is not considered part of the cabin. However smoking is usually not allowed according to general aviation rules everywhere. Not even e-cigarettes are allowed. Why are e-cigs not allowed if they have no smoke you may ask?
Reason is that many people might see someone using an e-cig and think that it's ok to smoke, hence lighting up a real one. This has happened before.
I've even had faulty no smoking lights on flights and passengers thinking that smoking in that specific area of the plane where the light is faulty is fine.
When travelling people tend to pack so much stuff for their trips but leave the most vital thing behind - their brains!


text:
Comparing a Flight In Turbulent Conditions At Va And Vb
First, let's cover definitions for both airspeeds:

Turbulence penetration airspeed (Vb) is the design speed for maximum gust intensity (i.e. the intersection between the 66 fps gust line and the maximum certified g load of the aircraft).
Maneuvering speed (Va) is defined as the speed at which the aircraft reaches its maximum positive load factor limit at the same time it experiences an aerodynamic stall when flight controls are fully deflected in flight (or when encountering a vertical gust).

After both definitions, shouldn't be more logical to fly in turbulent conditions at Va, since any encountered gust would give you maximum and equal margin from overstressing the airframe and stalling the aircraft?
For example, if turbulence penetration speed (Vb) is greater than Va for your specific aircraft, and you encounter severe turbulence while flying at Vb, that would mean that a potentially hazardous gust of wind would overstress the airframe first and therefore, not provide maximum protection from damaging the aircraft?
On the other hand, if Vb is smaller than Va and assuming the same scenario as described above, you would first stall the aircraft (which again does not provide maximum protection in turbulence)?
Additional: What is the exact difference between Vb and Vra (Rough Air Speed), if any?

Can you give a specific example of an aircraft with a Vb greater (or less) than Va?

Sure. For example, Bombardier Dash 8 Q400 series has Va of 204 kts and Vb of 210 kts. Although the difference is small, Va is never the same as Vb for any transport aircraft as far as I know.

Related: When to slow down to Va for turbulence?.

The requirements for VA and VB can be found in Code of Federal Regulations, more precicely in Title 14, Chapter I, Subchapter C, Part 25, Subpart C, Flight Maneuver and Gust Conditions § 25.335

(c) Design maneuvering speed VA. For VA, the following apply: [sic]
(1) VA may not be less than VS1 √n where—
(i) n  is the limit positive maneuvering load factor at VC; and
(ii) Vs1  is the stalling speed with > flaps retracted.
(2) VA  and VS must be evaluated at the design weight and altitude under consideration.
(3) VA  need not be more than VC or the speed at which the positive CN max curve intersects the positive maneuver load factor line, whichever is less.

...

(d) Design speed for maximum gust intensity, VB.
(1) VB may not be less than

where—
VS1 = the 1-g stalling speed based on CNA max with the flaps retracted at the particular weight under consideration;
Vc = design cruise speed (knots equivalent airspeed);
Uref = the reference gust velocity (feet per second equivalent airspeed) from § 25.341(a)(5)(i);
w = average wing loading (pounds per square foot) at the particular weight under consideration.

ρ = density of air (slugs/ft3);
c = mean geometric chord of the wing (feet);
g = acceleration due to gravity (ft/sec2);
a = slope of the airplane normal force coefficient curve, CNA per radian;
(2) At altitudes where VC is limited by Mach number—
(i) VB may be chosen to provide an optimum margin between low and high speed buffet boundaries; and,
(ii) VB need not be greater than VC.

Now, as you can see the formula for VA is pretty straightforward, whereas the one for VB is more complicated. While I have not tested these formulas, I'm quite certain the simple reason for the  seemingly illogical VA and VB values simply stem from the way they are "regulated".
 sorry for using pictures for formulas, proved too difficult for me to get them here in anynother way